1. Field of the Invention
The present invention relates to a package for housing an optical semiconductor element for use in the optical communication fields and so forth, and to an optical semiconductor apparatus.
2. Description of the Related Art
Shown in FIG. 5 is an example of a conventional optical semiconductor apparatus that air-tightly accommodates therein an optical semiconductor element operating at high frequencies, such as an optical semiconductor laser (LD) or a photodiode (PD), in the optical communication fields and so forth. FIG. 5 is a sectional view of an optical semiconductor apparatus that accommodates therein an LD as an optical semiconductor element. In FIG. 5, reference numeral 21 represents a base body; 22 represents an optical semiconductor element; 23 represents a metal-made lid body; 24 represents a light-transmitting member; and 26 represents an optical fiber.
The optical semiconductor apparatus shown in FIG. 5 includes a platy base body 21 made of a metal; a lid body 23 made of a metal; a light-transmitting member 24. The lid body 23 is formed in a cylindrical shape, which includes an upper end face 23a having a through hole 23b formed at the center thereof, and a lower end 23c which is left opened and joined to the outer periphery of the upper principal surface of the base body 21. The light-transmitting member 24 is bonded around the upper end face 23a-side opening of the through hole 23b. Moreover, a through bore 21a is drilled all the way through from the upper principal surface to the lower principal surface of the base body 21. Fitted into the through bore 21a is an input/output terminal 25.
The input/output terminal 25 includes a plate portion 25b made of a dielectric substance; an upright wall portion 25a made of a dielectric substance; a line conductor 25c; and a metal plate 30. The plate portion 25b has, on its top surface, the line conductor 25c formed so as to extend from one edge to another edge opposite thereto of the top surface. The upright wall portion 25a is joined to the top surface of the plate portion 25b, with the line conductor 25c sandwiched therebetween. The input/output terminal 25 is constituted in such a manner that the plate portion 25b and the upright wall portion 25a are mounted on the metal plate 30. An optical semiconductor element 22 is mounted, through a base 28 made of an aluminum nitride (AlN) ceramic, at the front end of the metal plate 30 which faces an inside of the optical semiconductor apparatus.
The base body 21 is formed of a disk- or rectangular-shaped plate made of a metal such as an iron (Fe)-nickel (Ni)-cobalt (Co) alloy or a copper (Cu)-Tungsten (W) alloy. The base body 21 has the through bore 21a drilled all the way through from the upper principal surface to the lower principal surface thereof, for inserting thereinto the input/output terminal 25 composed of the plate portion 25b made of a dielectric substance such as an alumina (Al2O3) ceramic; the upright wall portion 25a made of a dielectric substance such as an Al2O3 ceramic; and the metal plate 30 joined to a lower surface of the plate portion 25b. The input/output terminal 25 is inserted into the through bore 21a for bringing the optical semiconductor apparatus into conduction externally. A brazing filler material such as silver (Ag) brazing filler is charged into a gap between the input/output terminal 25 and the through bore 21a, so that the base body 21 and the input/output terminal 25 may be hermetically joined to each other by brazing. With the metal plate 30, heat emanating from the optical semiconductor element 22 can be transmitted to the base body 21 satisfactorily, and then dissipated from the base body 21 and the lid body 23 satisfactorily. Hence, good heat dissipation can be provided and thus the optical semiconductor element 22 exhibits higher operation reliability.
Moreover, the plate portion 25b and the upright wall portion 25a of the input/output terminal 25 are fabricated as follows. For example, in the case of using an Al2O3 ceramic, at first, a suitable organic binder, plasticizer, or solvent is mixedly added to powder of a base material such as aluminum oxide, silicon oxide (SiO2), magnesium oxide (MgO), or calcium oxide (CaO), to form a slurry. The slurry is then formed into a plurality of ceramic green sheets in accordance with a conventionally-known tape forming technique such as a doctor blade method or calendar roll method. Next, a suitable organic binder, plasticizer, or solvent is mixedly added to powder of a high-melting-point metal, such as W or molybdenum (Mo), to form a metal paste. The metal paste is then print-coated onto the ceramic green sheet in accordance with a thick-film forming technique, such as a screen printing method, to form a metallized wiring layer acting as the line conductor 25c with a predetermined pattern. Moreover, the plate portion 25b has its lower surface wholly print-coated with a metallized layer so that the metal plate 30 may be brazed thereto with use of Ag brazing filler or the like material. After that, a plurality of ceramic green sheets are stacked one upon another, and the stacked body is fired in a reducing atmosphere at a temperature an high as approximately 1600° C. In this way, the line conductor 25c is formed in the input/output terminal 25, with the characteristic impedance matched properly.
The metal plate 30 is formed in a rectangular shape and is made of a metal such as an Fe—Ni—Co alloy or Cu—W alloy. By subjecting an ingot of such a metal to a conventionally-known metal processing method, such as a rolling process or die cutting process, the metal plate 30 is formed in a predetermined configuration. On the principal surface of the metal plate 30 on which the plate portion 25b is mounted, the rectangular parallelepiped base 28 made of an AlN ceramic is brazed to the front end thereof facing an inside of the optical semiconductor apparatus with use of Ag brazing filler or the like material, for mounting thereon the optical semiconductor element 22.
Moreover, at the outer periphery of the upper principal surface of the base body 21 is disposed the cylindrically shaped lid body 23 composed of the upper end face 23a having the through hole 23b formed at the center thereof and the lower end left opened. The lower end 23c of the lid body 23 is air-tightly joined to the base body 21 by welding or soldering using solder such as lead (Pb)-tin (Sn) solder.
The cylindrically shaped lid body 23 has a circular or polygonal, such as rectangular, sectional profile (cross-sectional profile). The lid body 23 is formed in a predetermined configuration by subjecting an ingot of a metal such as an Fe—Ni—Co alloy to a conventionally-known metal processing method such as the rolling process or die cutting process.
In the lid body 23, the light-transmitting member 24 is bonded around the upper end face 23a-side opening of the through hole 23b so as to stop up the through hole 23b by glass bonding or soldering. The light-transmitting member 24 is made of glass or sapphire having the shape of a disk, lens, sphere, or hemisphere.
Moreover, the optical fiber 26 is fixed onto an upper end face of a cylindrically shaped fixing member 27 made of a metal such as an Fe—Ni—Co alloy. The metal-made fixing member 27 has its lower end face welded to the outer peripheral surface of the lid body 23 by laser welding or the like method. Upon the optical fiber 26 being fixed above the light-transmitting member 24 by the metal-made fixing member 27, the optical semiconductor apparatus is available as a finished product. Whereupon, optical signals are transferable between the optical semiconductor element 22 contained within the optical semiconductor apparatus and the outside thereof through the optical fiber 26 (for example, refer to Japanese Unexamined Patent Publication JP-A 2003-198028).
In the conventional construction, however, in achieving sealing, the input/output terminal 25 cannot be joined to the base body 21 without being inserted into the through bore 21a. Therefore, the through bore 21a, as well as the metal plate 30, the plate portion 25b, and the upright wall portion 25a of the input/output terminal 25, need to be designed with high dimensional and assembly accuracy. This necessitates an additional process in the processing on the through bore 21a and the input/output terminal 25 to attain high dimensional accuracy, and thus leads to poor mass-productivity of the base body 21 and the input/output terminal 25.
In addition, the input/output terminal 25 projects beyond a lower surface of the base body 21, which results in the difficulty in satisfying the recent demand for further miniaturization.